The population of the world’s largest king penguin colony, which resides on Île aux Cochons, a remote French island in the subantarctic Crozet Archipelago, has plummeted by a staggering 90 percent since the 1980s, according to a new study published in the Antarctic Science journal.
Using recent satellite images and photos captured from helicopters, researchers measured the changes in the size of the colony since the island was last visited by scientists in the early 1980s. The penguin population back then had included some 500,000 breeding pairs and over 2 million individuals, the scientists said. Today, the number of breeding pairs has shrunk to just 60,000. About 200,000 individuals remain.
“It is completely unexpected, and particularly significant since this colony represented nearly one-third of the king penguins in the world,” Henri Weimerskirch, the lead author of the study and an ecologist at the Center for Biological Studies in Chize, France, told Agence France-Presse.
Weimerskirch shared a photograph with the news outlet that shows the island swarming with penguins in 1982:
Troublingly, Weimerskirch and his colleagues said they have no idea what’s caused the colony’s dramatic collapse — though they’ve floated a number of theories.
Climate change is one possible factor. Researchers said the decline appears to have begun in the late 1990s when a strong El Niño weather event warmed the southern Indian Ocean and impacted the colony’s food supply. Since then, the Earth has endured several more El Niño events, as well as several of the warmest years on record.
Earlier studies conducted by Weimerskirchand other researchers have shown how global warming ― if it continues at its current pace ― will pose a major threat to king penguins living in the Crozet Archipelago in the coming decades.
SEE: Animals that recently went extinct:
Weimerskirch and his colleagues, however, said they don’t believe they can blame climate change alone for the recent collapse of the Île aux Cochons colony as king penguin populations on nearby islands have remained either stable or, in some cases, have even increased, over the past few decades.
The researchers believe, therefore, that the cause of the population decline on the island must be location-specific, noted ScienceAlert.
Overcrowding, they said, could be another factor, as could a disease or tick infestation. Invasive species like house mice and feral cats, which are known to exist on the island, could also be impacting the health of the colony, the researchers theorized.
Ultimately, the team said they will need to go to the island themselves before they can figure out what’s really going on. Weimerskirch said he hopes researchers will be able to visit the colony in 2019.
“The cause of the massive decline of the colony remains a mystery, and needs to be resolved,” the researchers wrote in the paper. “Although the decline started at least 20 years ago, it appears to be ongoing, and the causes of the decline may still be active.”
After the Emperor penguin, king penguins are the largest penguin species on Earth.
There are two subspecies of king penguin: the Aptenodytes patagonica patagonicus, which inhabits the Falklands, South Georgia Island and in southern Chile; and A. patagonicus halli, which lives in the Crozet Archipelago, as well as on Heard, Kerguelen, Macquarie and Prince Edwards islands.
King penguin females lay one egg at a time and the parents take turns incubating it on their feet.
The International Union for Conservation of Nature currently lists king penguins as a species of “least concern.” The newly published study, however, may “prompt a reevaluation” of this status, reported AFP.
This article originally appeared on HuffPost.